Cellulosic webs, such as non-woven or paper tissue webs, find extensive use in modern society. Facial tissues, toilet tissues, kitchen paper or tissue handkerchiefs are staple items of commerce.
Among the most important physical properties of these products are their strength, their softness, their absorbency, primarily for aqueous systems, and their lint resistance.
Tissue paper products are often exposed to extremely varied strength requirements in the wet and dry states. For instance, it must be ensured, in the case of household paper (kitchen towels) that they retain their strength at least for a specific period of time when exposed to aqueous liquids or moisture-containing food. On the other hand, toilet paper should dissolve in water, some time after use, in order to prevent the sewage systems from clogging up. At the same time, toilet paper must not immediately use its strength properties during use for apparent reasons. Correspondingly, the prior art makes a distinction between dry strength and wet strength properties, the latter being divided in further categories such as initial wet strength, temporary wet strength and permanent wet strength depending on the point of time of measuring the wet strength after re-wetting a dry tissue paper.
A paper of an untreated cellulose-containing fibrous material usually looses 95% to 97% of its dry strength when saturated with water so that it normally cannot be used in the moistened or wet state. This is due to the fact that the paper develops dry strength as a result of inter-fibre hydrogen bonds which are broken up by water.
The use of wet strength resins, such as polyamidoamine-epichlorohydrine resin is a widely known counter measure, However, if these resins are used alone, they typically lead to tissue paper which is fairly stiff and has almost the haptic properties of normal paper.
The isolated use of softeners such as the typically employed quaternary ammonium compounds, on the other hand, reduces the strength since softeners also interact with inter-fibre hydrogen bonds, Further, they can decrease the absorbency due to hydrophobic effects.
These are typical examples for the generally occurring problem in the art of tissue paper making that the above-mentioned four properties conflict each other in so far as attempts to improve one property can be detrimental for another.
Therefore, the prior art describes many processes for achieving a suitable balance of softness, strength (dry and wet strength), lint properties and absorbency which shall be exemplified in the following.
WO 00/39398 relates to chemically modified cellulosic materials that can have improved properties such as wet strength, softness or absorbency. This document discloses a process comprising:                a) chemically attaching anionic groups, preferably carboxymethyl groups, via etherification to the surface of a cellulosic web fibre, for instance by, an alkaline treatment with sodium chloroacetate, and        b) adding one or more cationic additives prior to web forming to form an ionic association between the cationic additive and the anionic fibre and        c) forming a wet-laid sheet.        
The cationic additive is selected from the group consisting of a wet strength resin, a debonder, a softening agent, a dewatering aid and a sizing agent.
However this technique is cumbersome, since it requires pre-reacting the pulp with an anionic groups-forming reagent (preferably a carboxymethyl-forming reagent) prior to sheet forming processes.
The process according to U.S. Pat. No. 5,316,623 is intended to provide a better absorbency as well as better wet and dry strength in paper towels or other tissue products. According to the teaching of this document, the following three ingredients are to be combined:
(A) a neutral or alkaline-curing thermosetting wet strength resin obtainable by reacting epichlorohydrine with polyaminoamide, polyamine or an aminopolymer.
(B) a water-soluble anionic polymer containing carboxyl groups or carboxylate ions such as carboxymethyl cellulose, and
(C) a non-thermosetting tertiary amino polyamide-epichlorohydrine resin.
U.S. Pat. No. 3,755,220 discloses soft cellulosic sheet materials having an improved ratio of wet tensile strength to dry tensile strength. This is achieved by including in the papermaking furnish at least one water-soluble, thermosetting cationic resin, such as polyamide-epichlorohydrin resin and at least one debonder including anionic and cationic surface-active agents, in particular cationic, quaternary ammonium compounds.
EP 0 672 781 A2 discloses pre-wettable high softness paper having temporary wet strength. According to the teaching of this document, temporary wet strength agents and cationic nitrogenous softeners are preferably combined.
U.S. Pat. No. 5,573,637 discloses a multi-layered tissue paper product comprising a softener composition (quaternary ammonium compound and polysiloxane) and binders materials, either wet strength binders, such as polyamido-epichlorohydrine resins and/or dry strength binders such as carboxyethyl cellulose (CMC) where the majority of the softener composition is contained in the outer layers.
U.S. Pat. No. 3,998,690 relates to a process for the preparation of fibrous assemblies such as paper having advantageous properties such as wet strength, absorbency, softness, good drape and enhanced bulk which exhibit compaction resistance.
The process for the preparation of these fibrous assemblies comprises the steps of                a. forming separate anionically charged and cationically charged fibre slurry aliquots,        b. mixing the anionically and cationically charged aliquots,        c. collecting the resulting discrete fibre aggregates and        d. draining and drying said aggregates.        
The cationic materials for the practice of this invention include quaternary ammonium compounds and common wet strength additives, such as aminopolyamide reaction products with epichlorohydrine. Carboxyethyl cellulose is mentioned as one among many additives for anionically charging the fibres.
U.S. Pat. No. 5,437,766 aims at providing soft, absorbent, lint resistant multiply-tissue paper products. For this purpose                a. paper making fibres are treated with        b. a biodegradable quaternary ammonium compound        c. a water soluble polyhydroxy compound        d. a wet strength binder, for instance, polyamide epichlorohydrine resins, and        e. a. dry strength binder, for instance, carboxymethyl cellulose.        
The majority of the softener composition (biodegradable quaternary ammonium compound and polyhydroxy compound) is contained in the outer layers of the plies
According to the examples of this US Patent, two individually treated furnish streams are kept separate through the headbox and deposited onto a fourdrinier wire to form a two layer embryonic web.
The inner layer is prepared from a gently refined NSK (northern softwood Kraft) fibre slurry to which 2% Kymene wet strength resin and 1% CMC were given.
The second slurry being intended for the outer layer is prepared from eucalyptus fibres which were treated with Kymene, CMC and a 1% solution of the above-explained chemical softener mixture.
U.S. Pat. No. 6,162,327 discloses in its examples the use of similar treatment chemicals with the difference that Kymene, CMC and chemical softening mixture can be added to the NSK slurry.
It is an object of the present invention to provide a simple process for the preparation of fibrous webs, such as tissue paper having a high wet strength and simultaneously a suitable balance of other properties relevant for the web, such as dry strength, softness, bulk and absorbency.
It is a further object of the present invention to provide such fibrous web, in particular tissue paper.